Light irradiation apparatus and information rewritable system

ABSTRACT

A light irradiation apparatus includes an irradiation unit including a light source to emit light to a process-target object, a light source driving circuit to drive the light source, a light source controller to control the light source driving circuit to change a light output level of the light source, and a light spot controller to control energy or energy density of a beam spot of the light on the process-target object depending on an operation mode, and a transition mode that one operation mode is being changed to another mode. The light spot controller sets the energy or energy density during the transition mode lower compared to either of the energy or energy density during the one operation mode before the transition mode and the energy or energy density during the another mode after the transition mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 15/184,369, filed on Jun. 16, 2016, which claims prioritypursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No.2015-134513, filed on Jul. 3, 2015, and Japanese Patent Application No.2016-013169, filed on Jan. 27, 2016, the disclosure of which areincorporated by reference herein in their entirety.

BACKGROUND Technical Field

The disclosure relates to a light irradiation apparatus, and aninformation rewritable system including the light irradiation apparatus.

Background Art

Light irradiation apparatuses that irradiate light to process-targetobjects have been developed, and the light irradiation apparatusincludes a light source driving circuit. For example, a light emittingdiode (LED) driving circuit including a LC filter (output filter)including a coil and a capacitor is used as the light source drivingcircuit. However, if the LED driving circuit is employed for the lightirradiation apparatus, and a light output level is changed by using theLED driving circuit, unintended “structural transformation” may occur tothe process-target object. The unintended “structural transformation”means, for example, color change, melting, and shape change of theprocess-target object, which may be caused by irradiating theprocess-target object with light having an output level not suitable forprocessing.

SUMMARY

As one aspect of the present invention, a light irradiation apparatus isdevised. The light irradiation apparatus includes an irradiation unitincluding a light source to emit light to a process-target object, alight source driving circuit to drive the light source, a light sourcecontroller to control the light source driving circuit to change a lightoutput level of the light source, and a light spot controller to controlenergy or energy density of a beam spot of the light on theprocess-target object depending on an operation mode, and a transitionmode that one operation mode is being changed to another mode. The lightspot controller sets the energy or energy density during the transitionmode lower compared to either of the energy or energy density during theone operation mode before the transition mode and the energy or energydensity during the another mode after the transition mode.

As another aspect of the present invention, a light irradiationapparatus is devised. The light irradiation apparatus includes anirradiation unit including a light source to irradiate laser light to aprocess-target object, a light source driving circuit to drive the lightsource, a light source controller to control the light source drivingcircuit to change a light output level of the light source, and atravelling direction controller to control a travelling direction of thelight emitted from the light source depending on an operation mode, anda transition mode that one operation mode is being changed to anothermode. The travelling direction controller controls the travellingdirection of the light during the transition mode to a direction thatthe light does not irradiate the process-target object.

As another aspect of the present invention, a light irradiationapparatus is devised. The light irradiation apparatus includes anirradiation unit including a light source to irradiate light to aprocess-target object, a light source driving circuit to drive the lightsource, a light source controller to control the light source drivingcircuit to change a light output level of the light source, a lightshielding member moveable between a light block position to block thelight emitted from the light source at least partially, and a retractionposition retracted from the light block position, and a positioncontroller to control a position of the light shielding member at thelight block position during the transition mode.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages and features thereof can be readily obtained and understoodfrom the following detailed description with reference to theaccompanying drawings, wherein:

FIG. 1 illustrates a schematic overall configuration of a lightirradiation apparatus of a first example embodiment;

FIG. 2 illustrates a schematic overall configuration of the lightirradiation apparatus of the first example embodiment;

FIG. 3 is an example of a block diagram of a hardware configuration ofthe light irradiation apparatus of FIG. 1;

FIG. 4 is an example of a light source drive circuit;

FIG. 5 is an example of change of drive current;

FIG. 6 is an example of a profile of light output level when a lightoutput is changed;

FIG. 7 is an example of unintended structural transformation when theimage recording and the image erasing are performed using unstablelight;

FIG. 8 is a flowchart illustrating the steps of laser light irradiationmethod of the first example embodiment;

FIG. 9 illustrates a schematic overall configuration of a lightirradiation apparatus of a second example embodiment;

FIG. 10 illustrates a schematic configuration of an aperture stop thatcan adjust an aperture size;

FIG. 11 illustrates a schematic overall configuration of a lightirradiation apparatus of a third example embodiment;

FIG. 12 is a flowchart illustrating the steps of laser light irradiationmethod of the third example embodiment;

FIG. 13 illustrates a schematic overall configuration of a lightirradiation apparatus of a fourth example embodiment;

FIG. 14 illustrates a schematic overall configuration of a lightirradiation apparatus of a fifth example embodiment;

FIG. 15 illustrates a schematic overall configuration of a lightirradiation apparatus of a sixth example embodiment;

FIG. 16 is a flowchart illustrating the steps of laser light irradiationmethod of the sixth example embodiment;

FIG. 17A illustrates structural transformation of a reversible thermalrecording medium;

FIG. 17B illustrates mechanism of coloring and decoloring of thereversible thermal recording medium;

FIG. 18 is a schematic graph of an average output of a light source;

FIG. 19 is a block diagram of a main controller of a seventh exampleembodiment;

FIG. 20 is a flowchart illustrating the steps of a process ofcontrolling irradiation power or irradiation power density when a lowerduty ratio mode is selected;

FIG. 21 is a flowchart illustrating the steps of a process ofcontrolling irradiation power or irradiation power density when a swingmode is selected;

FIG. 22A is a control timing chart for a lower duty ratio mode;

FIG. 22B is a control timing chart for a swing mode; and

FIG. 23 is a flowchart illustrating the steps of a process ofcontrolling irradiation power or irradiation power density when acombined mode (lower duty ratio mode+swing mode) is selected as theoperation mode.

The accompanying drawings are intended to depict exemplary embodimentsof the present invention and should not be interpreted to limit thescope thereof The accompanying drawings are not to be considered asdrawn to scale unless explicitly noted, and identical or similarreference numerals designate identical or similar components throughoutthe several views.

DETAILED DESCRIPTION

A description is now given of exemplary embodiments of the presentinvention. It should be noted that although such terms as first, second,etc. may be used herein to describe various elements, components,regions, layers and/or sections, it should be understood that suchelements, components, regions, layers and/or sections are not limitedthereby because such terms are relative, that is, used only todistinguish one element, component, region, layer or section fromanother region, layer or section. Thus, for example, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

In addition, it should be noted that the terminology used herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the present invention. Thus, for example, asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Moreover, the terms “includes” and/or “including”, when usedin this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Furthermore, although in describing views shown in the drawings,specific terminology is employed for the sake of clarity, the presentdisclosure is not limited to the specific terminology so selected and itis to be understood that each specific element includes all technicalequivalents that operate in a similar manner and achieve a similarresult. Referring now to the drawings, apparatus or system according toone or more example embodiments are described hereinafter.

A description is given of according to one or more example embodimentsof the present invention, in which parts having the same configurationand capability are assigned with the same references.

FIRST EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 100 of a firstexample embodiment with reference to FIGS. 1 to 8. The light irradiationapparatus 100 can use various lights such as laser light.

FIGS. 1 and 2 illustrate a schematic overall configuration of the lightirradiation apparatus 100 of the first example embodiment. FIG. 3 is anexample of a block diagram of a hardware configuration of the lightirradiation apparatus 100.

For example, the light irradiation apparatus 100 can be used as anapparatus that irradiates light (e.g., laser light) to a reversiblethermal recording medium RM used as a process-target object to recordand erase image information on the reversible thermal recording mediumRM as illustrated in FIG. 1. Hereinafter, the reversible thermalrecording medium may be simply referred to the “medium.”

The light irradiation apparatus 100 can be used for an informationrewritable system. For example, the light irradiation apparatus 100 canbe a laser-use recording/erasing apparatus used as rewritable lasersystem, which is an example of the information rewritable system. Theinformation rewritable system such as the rewritable laser systemincludes, for example, the light irradiation apparatus 100, a transportunit such as a conveyor belt to convey transport-use containers attachedwith reversible thermal recording media, a control unit, and a monitorincluding a touch panel.

The light irradiation apparatus 100 can record or write, and eraseinformation such as image information repeatedly to the reversiblethermal recording medium RM (e.g., label) attached to the transport-usecontainers such as corrugated cardboards and plastic containers withoutcontacting the reversible thermal recording medium RM. Therefore, thelight irradiation apparatus 100 can be applied to the logistics deliverysystem, in which image information can be written and erased on labelsattached to corrugated cardboards and/or plastic containers beingconveyed by the transport unit such as a conveyor belt without stoppingthe conveyor line, with which the shipment time can be shortened.Further, without detaching the labels from the corrugated cardboards andplastic containers, the corrugated cardboards and plastic containers canbe re-used by erasing and writing image information on the labels.

As illustrated in FIGS. 1 to 3, the light irradiation apparatus 100includes, for example, a casing 15, an optical unit 30 including a lightsource unit 11, a collimator lens 12 b, a diffusing lens 16, acondensing lens 18 and a light scanning unit 13, a focus positioncontrol unit 40, a control system 50, an information setting unit 60, arange finder 70, a temperature sensor 80, and a program unit 90.

Light (e.g., laser light) emitted from the light source unit 11 isconverted by the collimator lens 12 b to parallel light, diffused by thediffusing lens 16, and then focused on the light scanning unit 13 by thecondensing lens 18. The light scanning unit 13 deflects the light comingfrom the condensing lens 18 to scan the light on the reversible thermalrecording medium RM. In this example case, the condensing lens 18includes two lenses, but the condensing lens 18 can be composed one lensand three of more lenses.

As illustrated in FIG. 2, a focus position of the diffusing lens 16 canbe changed. Specifically, as illustrated in FIG. 2, the focus positioncontrol unit 40 includes a lens driver 17, which can move the diffusinglens 16 along the light-axis direction. The lens driver 17 includes, forexample, a pulse motor, and can move the diffusing lens 16 with a highspeed to control the focus position of the diffusing lens 16 with thehigh speed. Further, by controlling the focus position of the diffusinglens 16, the focus position of the optical unit 30 can be controlled,and a beam spot diameter on a process-target object can be controlled(i.e., energy density of beam spot on the process-target object can becontrolled). The “energy density” is the light intensity or energy ofbeam spot per unit area. The lens driver 17 can be controlled by thecontrol system 50.

(Control system)

The control system 50 includes, for example, a direct current (DC) powersource used as a driving power source of the light source unit 11 (seeFIG. 4), a driving power source of a galvanometer, a power source forcooling Peltier device, a main controller 50 a (see FIG. 3), and a lightsource drive circuit 50 b such as a laser drive circuit to drive thelight source unit 11 (see FIG. 3). The main controller 50 a includes,for example, a central processing unit (CPU) and a chip set.

The main controller 50 a outputs an emission trigger signal and a lightoutput level (or light-output setting value) matched to the imagerecording to the light source drive circuit 50 b when the imagerecording is performed, and outputs an emission trigger signal and alight output level (or light-output setting value) matched to the imageerasing to the light source drive circuit 50 b when the image erasing isperformed.

The light source drive circuit 50 b applies a driving current, matchedto the light output level received from the main controller 50 a, to thelight source unit 11.

(Program unit)

The program unit 90 can be used to input and edit information forperforming the image recording and erasing by using a touch panel and akeyboard as an input device. Specifically, the program unit 90 can beused to input operation conditions such as an output level of light andlight scan speed, and to generate and edit data to be recorded forperforming the image recording and erasing.

(Light source unit)

The light source unit 11 employs, for example, YAG laser, fiber laser,semiconductor lasers such as laser diode (LD) and vertical cavitysurface emitting laser (VCSEL), and fiber-coupled laser. For example,the laser recording can generate a recording image having highervisibility by irradiating laser light onto a recording area of thereversible thermal recording medium evenly to heat the recording areaevenly. Typically, the laser light has the Gaussian distribution thatthe light intensity is higher at the center of the distribution.Therefore, if the laser light having the Gaussian distribution is usedfor the image recording, the contrast at peripheral areas of imagebecomes lower than the contrast at the center of image, with whichvisibility of image becomes lower, and thereby the image qualitydeteriorates.

In view of this issue of uneven image contrast, an optical element forchanging the light distribution such as non-spherical lens anddiffractive optical element (DOE) can be disposed in the light path toprevent this uneven image contrast, but the apparatus cost becomeshigher, and the optical designing to avoid the light distributiondistortion caused by aberration becomes difficult.

In view this issue, the fiber-coupled laser can be employed withoutusing the optical element for changing the light distribution, in whichlaser light emitted from an end of fiber can be shaped into a top-hatshaped laser light easily, and the image recording can be performed withhigher visibility. Therefore, the fiber-coupled laser can be usedpreferably.

A preferable wavelength of the laser light emitted from the light sourceunit 11 can be set based on property of light-to-heat convertingmaterial added to the reversible thermal recording medium, anddurability of the light-to-heat converting material for repeated imageprocessing.

(Light scanning unit)

The light scanning unit 13 can employ various configurations as long asthe laser light can scan the reversible thermal recording medium twodimensionally, which can be selected as required. For example, the lightscanning unit 13 can use a galvano scanner, a polygon scanner, and amicro electro mechanical systems (MEMS) scanner. In this description,the light scanning unit 13 employs a combination of two galvano scanners13 a and 13 b to scan the reversible thermal recording medium RM twodimensionally such as X direction (e.g., horizontal direction) and Ydirection (e.g., vertical direction). Each of the galvano scanners 13 aand 13 b includes a galvanometer and a galvano mirror attached to thegalvanometer. The light scanning unit 13 can be controlled by the maincontroller 50 a.

(Focus position control unit)

The focus position control unit 40 includes a lens system including atleast one lens (e.g., diffusing lens 16) disposed at a position betweenthe light source unit 11 and the light scanning unit 13, and a positionof the lens can be adjusted along the light-axis direction. By adjustingthe position of the lens, the focus position of the laser light comingfrom the optical unit 30, which is the focus position of the opticalunit 30, can be controlled.

When the image erasing is performed, the main controller 50 a controlsthe position of the diffusing lens 16 by using the focus positioncontrol unit 40 so that the laser light coming from the optical unit 30is de-focused on a position of the reversible thermal recording medium.With employing this configuration, the beam spot diameter on thereversible thermal recording medium becomes larger. For example, theimage on the reversible thermal recording medium can be erased faster orquickly by scanning the beam in the X direction alone (one dimensionalscanning) by activating the galvano scanner 13 b alone disposed at theexit end of the optical unit 30. Further, the image on the reversiblethermal recording medium can be erased faster or quickly by scanning thebeams in Y direction alone (one dimensional scanning) by activating thegalvano scanner 13 a alone.

By contrast, when the image recording is performed, the main controller50 a controls the position of the diffusing lens 16 by using the focusposition control unit 40 so that the laser light coming from the opticalunit 30 is focused on a position of the reversible thermal recordingmedium. With employing this configuration, the image recording can beperformed on the reversible thermal recording medium by scanning thebeams two dimensionally (i.e., X direction and Y direction) byactivating the galvano scanners 13 a and 13 b.

As to the reversible thermal recording medium RM used as theprocess-target object, an irradiation power density “DL” when the imageerasing is performed, and an irradiation power density “DH” when theimage recording is performed have a relationship of “DL<DH.” Since thebeam spot diameter when the image erasing is performed becomes largerthan the beam spot diameter when the image recording is performed asabove described, an output level of laser light emitted from the lightsource unit 11 when the image erasing is performed is set greater than noutput level of laser light emitted from the light source unit 11 whenthe image recording is performed to secure the required irradiationpower density. However, if the beam spot diameter when the image erasingis performed is not so larger compared to the beam spot diameter whenthe image recording is performed, the output level of laser light whenthe image erasing is performed can be set at a level equal to or less ofthe output level of laser light when the image recording is performed.The “irradiation power density” means the energy density of laser lighton the reversible thermal recording medium.

(Information setting unit)

The information setting unit 60 can be used to input and set imageerasing information, image recording information, and information of therange (i.e., distance) between the reversible thermal recording mediumRM and an exit window 15 w of the light irradiation apparatus 100 (seeFIG. 2).

As to the image recording process and the image erasing process, thefocus position of the optical unit 30 is controlled based on a settingvalue of range (i.e., distance) between the reversible thermal recordingmedium RM and the exit window 15 w of the light irradiation apparatus100.

After the information setting unit 60 is used to generate a control fileincluding the image erasing information, the image recording informationand the range information, the information setting unit 60 transfers thecontrol file to the control system 50 so that the control system 50 cancontrol each of the galvano scanners 13 a and 13 b, and the light sourceunit 11.

Since information transferring is not performed between the imagerecording process and the image erasing process, the shift from theimage recording process to the image erasing process can be performedwith lesser time.

Since the information transferring from the information setting unit 60to the control system 50 can be performed before the transport-usecontainer reaches the position facing the light source unit 11, and whenthe transport-use container is stopped, the overall system can beoperated smoothly, which means a time loss may not occur to the systemoperation.

The image erasing information, the image recording information and therange information set by using the information setting unit 60 can beexecuted as one control file. With this configuration, the transferringtime of control file to the light source unit 11 can be set shorter, andthe image rewriting can be performed with a higher speed.

(Range finder)

The range finder 70 is used to find or detect a range (i.e., distance)between the reversible thermal recording medium RM and the exit window15 w of the light irradiation apparatus 100.

The range or distance between the reversible thermal recording medium RMand the exit window 15 w of the light irradiation apparatus 100 isreferred to “distance to work” (see FIG. 2), and the “distance to work”can be measured by using, for example, a scale, a sensor or the like.

The range finding (i.e., distance measurement) can be simplified whenthe reversible thermal recording medium is not inclined greatly, inwhich one portion of the reversible thermal recording medium is measuredto reduce the measurement cost. When the image recording is performed onthe reversible thermal recording medium inclined greatly, the rangefinding (i.e., distance measurement) is required to be performed at aplurality of portions of the reversible thermal recording medium, inwhich the range finding may be performed at three points.

The range finder 70 can employ various configurations, which areselectable as required. For example, the range can be measured by usinga range sensor.

The range sensor can be, for example, a non-contact range sensor and acontact sensor. The contact sensor may cause damage to a target medium,and may be difficult to measure the distance with higher speed, but thecontact sensor can be used for some cases. The non-contact range sensormay be preferable. The non-contact sensor may employ, for example, alaser-using sensor that can perform the range finding (i.e., distancemeasurement) correctly with higher speed, and the non-contact sensor canbe compact in size and is not expensive.

Since the reversible thermal recording medium RM may be inclined, theposition measured by the range sensor is preferably the center portionof the image recording area, corresponding to an average distance to thereversible thermal recording medium. When the range finding is performedat a plurality of portions, based on a result of the range finding atthe measured positions, the main controller 50 a assumes that thereversible thermal recording medium is being inclined threedimensionally, and corrects the focus position of the optical unit 30,controllable by the focus position control unit 40.

(Temperature sensor)

The temperature sensor 80 measures at least one of temperature of thereversible thermal recording medium and ambient temperature around thereversible thermal recording medium. The main controller 50 a controlsthe irradiation power based on a result measured by the temperaturesensor 80.

Since the image recording and the image erasing of the reversiblethermal recording medium are performed by applying heat, suitableirradiation power varies depending on temperature. Specifically, thelaser light is controlled to irradiate the light as follows. Forexample, when the temperature is higher, the irradiation power is setlower, and when temperature is lower, the irradiation power is sethigher.

The temperature sensor 80 can employ various configurations, which areselectable as required. For example, temperature can be measured byusing a temperature sensor.

The temperature sensor 80 can include, for example, an environmenttemperature sensor that measures ambient temperature, and a mediumtemperature sensor that measures temperature of the medium.

The environment temperature sensor can be, for example, a thermistorthat can measure temperature with high speed, higher precision andlesser cost.

The medium temperature sensor can be, for example, a radiationthermometer that can measure temperature without contacting a targetobject.

(Image recording process)

The image recording process can be performed based on the measureddistance or range to the reversible thermal recording medium.Specifically, the irradiation power of laser light is adjusted based onthe measured distance, and then the laser light irradiates thereversible thermal recording medium to apply heat to the reversiblethermal recording medium.

The irradiation power is proportional to a value of “Pw/V,” in which“Pw” indicates an the irradiation light power, which is the light powerof laser light irradiated on the reversible thermal recording medium,and “V” indicates the scan speed of laser light on the reversiblethermal recording medium. Therefore, the irradiation power can beadjusted by adjusting at least one of the scan speed of laser light (V)and irradiation light power (Pw), in which it is preferable to maintainthe value of “Pw/V” at the substantially constant level.

The irradiation power can be controlled as follows. Specifically, theirradiation power can be increased by decreasing the scan speed of laserlight or by increasing the irradiation light power while the irradiationpower can be decreased by increasing the scan speed of laser light or bydecreasing the irradiation light power.

The scan speed of laser light can be controlled by using any methods asrequired. For example, a method of controlling a rotation speed of amotor that drives a scan mirror can be used.

The irradiation light power of laser light can be controlled by usingany methods as required. For example, a method of changing thelight-output setting value (light output level), and a control method ofadjusting a peak power (i.e., pulse amplitude), ON time (i.e., pulsewidth) and duty (i.e., pulse width/pulse cycle) of drive signal (i.e.,pulse signal) for driving a light source (e.g., light source unit 11)can be used.

The light-output setting value can be changed by changing thelight-output setting value depending on a recording portion on thereversible thermal recording medium. As to the method of controlling thedrive signal by setting the pulse width, the pulse width can be changeddepending on a recording portion on the reversible thermal recordingmedium to adjust the irradiation light power.

If an image recorded on the reversible thermal recording medium iserased by applying heat by irradiating the laser light on the reversiblethermal recording medium, and then a new image is recorded on thereversible thermal recording medium right after the erasing process,problems such as image density decrease of a drawn image, durabilitydecrease due to repeated use may occur.

Further, when the image recording process is performed by using theconstant level of light power, problems such as thickening of linewidth, crushing of characters and symbols, image density decrease,decrease of readability of information code, and durability decrease dueto repeated use may occur.

When an image is to be recorded on the reversible thermal recordingmedium for the first time, or when an image is recorded on thereversible thermal recording medium after a long time elapses from thetime of last image erasing that applied heat to the reversible thermalrecording medium to erase an image and the heat was dissipated, the heatcan be dissipated from a heated area of a reversible thermal recordinglayer of the reversible thermal recording medium irradiated by the laserlight to a surrounding area of the reversible thermal recording layer,and thereby the reversible thermal recording layer can be cooledsufficiently.

By contrast, when an image is to be recorded on the reversible thermalrecording medium right after the image erasing process that has appliedheat to erase an image, the heat applied during the image erasingprocess may be accumulated in the reversible thermal recording medium.Since the heat is still accumulated on the reversible thermal recordingmedium, the heat also remains in the surrounding area of the heated areaof the reversible thermal recording layer. If a new image is recorded onthe reversible thermal recording medium under this condition, thereversible thermal recording layer is cooled slowly compared to a caseof recording an image on the reversible thermal recording medium afterthe reversible thermal recording layer is cooled sufficiently. Due tothis phenomenon, image density decrease may occur to a drawn image anddecrease of readability of information code may occur.

Further, when the image recording process is performed by using theconstant level of light power, the output level of laser light is set toa value in view of the heat-accumulated area having the smallest levelof heat so that the sufficient image density can be obtained for theentire of recording area. However, if this output level of laser lightis used to record an image on the heat-greatly-accumulated area, thereversible thermal recording layer is overheated. Due to thisphenomenon, crushing of characters and symbols, image density decrease,decrease of readability of information code, and durability decrease dueto repeated use may occur.

These phenomenon are more likely to occur if the time interval between aplurality of the image erasing process and the image recording processis set shorter to increase the throughput performable by one lightirradiation apparatus that performs both of the image erasing and theimage recording, which means, if the time interval between the end pointof the image erasing and the start point of the image recording is setshorter, these phenomenon are more likely to occur.

Further, the above described problems are more likely to occur to animage having a plurality of imaging lines close to each other comparedto a single imaging line not close to other imaging line. This may occurbecause the heated area of the reversible thermal recording layer usedforming for the single imaging line not close to other imaging line issmaller than the heated area of the reversible thermal recording layerused for forming the plurality of imaging lines close to each other. Ifthe heated area is smaller, the heat can be dissipated from the heatedarea to the surrounding area of the reversible thermal recording mediumfaster, and the reversible thermal recording layer can be cooled faster,and thereby the reversible thermal recording layer may not beoverheated.

As illustrated in FIG. 4, the light source drive circuit 50 b includes,for example, a direct current (DC) power source used as a power source,the light source unit 11 such as a laser diode (LD), a LC filter,switching elements SW1 to SW3, a light emission controller 107, acurrent sensor 102, a current detector 103, and a current controller104.

The LC filter is an example of an output filter including a coil L as aninductive element and a capacitor C as a capacitive element.

The switching element SW1 employs, for example, a transistor thatswitches electrical conduction and non-conduction between the LD and theLC filter.

The light emission controller 107 generates a light emission controlsignal such as a pulse signal based on the emission trigger signal andthe light output level transmitted from signal the main controller 50 a.The light emission controller 107 outputs the light emission controlsignal to the switching element SW1 to turn ON/OFF of the switchingelement SW1 to control the light emission using the LD. Specifically,when the switching element SW1 is turned ON, a drive current ILD (pulsecurrent) is applied to the LD to emit the light from the LD.

Since the main controller 50 a outputs one light output level when theimage recording is performed, and another light output level when theimage erasing is performed, which are different with each other, to thelight emission controller 107, one drive current I_(LD) used for theimage recording, and another drive current I_(LD) used for the imageerasing, which are different with each other, are applied to the LD.

The current sensor 102 is connected between the DC power source and theLC filter to detect the drive current I_(LD).

The current detector 103 detects a current value of the drive currentI_(LD) based on an output value of the current sensor 102 and ON time(i.e., pulse width of light emission control signal) of the switchingelement SW1 controlled by the light emission controller 107.

The switching element SW2 employs, for example, a transistor thatswitches electrical conduction and non-conduction between the DC powersource and the current sensor 102.

The switching element SW3 employs, for example, a transistor thatswitches electrical conduction and non-conduction between the LC filterand the ground (earth).

The main controller 50 a sets a threshold “Ith” for a set current valueof the LD based on the light output level, and outputs the threshold“Ith” to the current controller 104. Specifically, for example, the maincontroller 50 a sets one threshold “Ith” for the drive current I_(LD)when the image recording is performed, and sets another threshold “Ith”for the drive current I_(LD) when the image erasing is performed, whichare different thresholds.

The current controller 104 compares an output value of the currentdetector 103 and the threshold “Ith” received from the main controller50 a, and controls the switching elements SW2 and SW3 based on acomparison result. Specifically, as illustrated in FIG. 5, when theswitching element SW2 is ON and the switching element SW3 is OFF and thedrive current I_(LD) exceeds the threshold “Ith,” the switching elementSW2 is set OFF and the switching element SW3 is set ON. Further, whenthe drive current I_(LD) becomes less than the threshold “Ith,” theswitching element SW2 is set ON and the switching element SW3 is setOFF. With this configuration, each of the drive current I_(LD) can becontrolled close to the corresponding threshold “Ith,” and thereby thelight can be emitted from the LD with a stabilized light output levelwhen the image recording is performed and when the image erasing isperformed.

The operation of the light source drive circuit 50 b is similar to anon-isolated DC-DC converter using a synchronous rectification circuit.The power source voltage +V is chopped by the synchronous rectificationcircuit having SW2 and SW3, and then smoothed by the LC filter composedof the coil L and the capacitor C to obtain the stabilized drive currentI_(LD). The drive current I_(LD) is monitored constantly by the currentsensor 102 and the current detector 103, and the monitored drive currentI_(LD) is compared with the set current value by the current controller104, and the comparison result is fed back to a level of the ON dutyratio of the synchronous rectification circuit. The switching ofcontinuous wave (CW) drive and pulse drive of laser light is performedby SW1. Based on the light emission control signal, SW1 is switched, inwhich when SW1 is ON, the drive current I_(LD) having a rectangularpulse shape is supplied. Since the drive current I_(LD) that flows whenthe irradiating of laser light starts is determined by the end voltagesof the capacitive element C, the transition time period known assettling time such as several milliseconds (ms) to several tensmilliseconds (ms) is required to set the drive current I_(LD) within adesired range, but the LC filter can set a lower ripple compared to theL filter having only the coil L as the output filter, and the LC filtercan be compact in size. Further, if other light source driving circuitnot using the above configuration is used, when the light output levelsignal greater than the operation range (i.e., dynamic range) is input,the circuit may not be operated with a stabilized manner, and uncertaintime such as the settling time may occur.

As to the light irradiation apparatus 100 including the light sourcedrive circuit 50 b having the above described configuration, when theimage processing mode is switched between the image erasing processingand the image recording processing, the light output level is switchedbetween “P_(H)” and “P_(L)” as indicated in FIG. 6, in which “P_(H)” isindicated by a bold line and “P_(L)” is indicated by a thin line. Forexample, when the mode is switched from the image erasing to the imagerecording, the light output level is switched from “P_(H)” to “P_(L)”(P_(H)→P_(L)) as indicated in FIG. 6, and a transition time period “Ts”such as several milliseconds (ms) is required to obtain the stabilizedP_(L). Further, for example, when the mode is switched from the imageerasing to the image recording, the light output level is switched from“P_(L)” to “P_(H)” (P_(L)→P_(H)) as indicated in FIG. 6, and thetransition time period “Ts” such as several milliseconds (ms) isrequired to obtain the stabilized P_(H).

This transitional state also occurs when the light irradiation apparatus100 is activated and then the initial image erasing is performed for thefirst time (0→P_(H)), or when the light irradiation apparatus 100 isactivated and then the initial image recording is performed for thefirst time (0→P_(L)), in which the transition time period “Ts” such asseveral milliseconds (ms) is required to obtain the stabilized lightoutput level.

If the image recording is performed while the light output level isunstable, as illustrated in the upper part of FIG. 7 with a dotted line,a writing-started-timing image may not be generated or may be generatedpartially (image forming failure may occur). If this phenomenon occurswhen a target image such as a bar code or QR code (registered trademark)is formed, reading errors may occur, and transport-use containers may bedelivered to wrong address.

Further, if the image recording is performed while the light outputlevel is unstable, as illustrated in the lower part of FIG. 7 with adotted line, an image is not erased completely and a new image isoverwritten on the not-completely-erased image by performing the imagerecording. If this phenomenon occurs when a target image such as a barcode or QR code (registered trademark) is formed, reading errors mayoccur, and transport-use containers may be delivered to wrong address.

As previously described with reference to FIG. 2, one light irradiationapparatus such as the light irradiation apparatus 100 can perform bothof the image recording and the image erasing. The light irradiationapparatus 100 includes the focus position control unit 40 that canadjust the beam spot diameter of the laser light on the reversiblethermal recording medium and the output level of the laser light emittedfrom the light source unit 11 so that the irradiation power of the laserlight emitted from the light source unit 11 becomes suitable values forthe image recording and the image erasing.

To set the suitable output level of the laser light for the imagerecording and the image erasing, The control system 50 controls theposition of the diffusing lens 16 when the image erasing is performedand when the image recording is performed by using the focus positioncontrol unit 40, and also controls the position of the diffusing lens 16when the main controller 50 a changes the light output level(light-output setting value) during the transition time period “Ts2(seeFIG. 6), required for stabilizing the light output level of the LD.

Specifically, the position of the diffusing lens 16 is controlled to seta beam spot diameter with a value so that the irradiation power densityof the beam spot generated on the reversible thermal recording mediumduring the transition time period “Ts” becomes effectively smaller thanthe minimum irradiation power density Dth required for the “structuraltransformation” such as the image erasing or the image recording on thereversible thermal recording medium.

Specifically, the beam spot diameter during the transition time period“Ts” is set effectively greater than the beam spot diameter set for theimage recording and the image erasing.

With employing this configuration, the laser light can be irradiatedwith the irradiation power density not causing the “structuraltransformation” of the reversible thermal recording medium during thetransition time period “Ts” that is the time when the light output levelof the LD is being unstable.

The switching between the image erasing and the image recording such asthe image erasing→the image recording or the image recording→the imageerasing is not performed right after the one processing is completed. Acooling time Tc such as several tens milliseconds (ms) is required whenany one of the image recording and the image erasing is completed tocool the reversible thermal recording medium sufficiently.

Since the transition time period “Ts” defined by a time point when thelight output level is changed and a time point when the light outputlevel of the LD becomes stable is shorter than the cooling time Tc, thetact time may not increase even if the above described method isperformed.

For example, the light irradiation apparatus 100 can be set with twomodes for light energy modes, which can be switched from one to another.Specifically, the light irradiation apparatus 100 is set with twodifferent light energy modes (laser light irradiation modes) which canbe switched from one to another. The two modes includes, for example, anerasing mode and a recording mode. The erasing mode is used to scan thelaser light having light energy of about 100 [Watt] and the larger beamdiameter onto the reversible thermal recording medium. The recordingmode used to scan the laser light having light energy of about 20 [Watt]and the smaller beam diameter onto the reversible thermal recordingmedium.

(Mechanism of image recording and image erasing)

A description is given of “structural transformation” of the reversiblethermal recording medium. A mechanism of the image recording and theimage erasing can be devised by using reversible change of color tone byapplying heat, which can be devised by Leuco dye and reversibledeveloper (hereinafter, developer). The color tone changes reversiblybetween decolored (transparent) state and colored state by applyingheat.

FIG. 17A illustrates an example of change of states of the reversiblethermal recording layer including resin having the Leuco dye and thedeveloper as profile of temperature -color optical density, and FIG. 17Billustrates an example of a mechanism of coloring and de-coloring of thereversible thermal recording medium such as reversible change of colortone between the decolored (transparent) state and the colored state byapplying heat. As illustrated in FIG. 17B, the reversible thermalrecording medium can change its states between a decolored (transparent)state (A), a melted colored state (B), a colored state (C), shifting toa decolored state (D), and a decolored (transparent) state (E).

When the temperature of the reversible thermal recording layer at thedecolored (transparent) state (A) is increased, the Leuco dye and thedeveloper are meltingly blended at a melting temperature T1, and thenthe Leuco dye and the developer becomes the colored state such as themelted colored state (B). When the Leuco dye and the developer arecooled rapidly from the melted colored state (B), the temperature of thereversible thermal recording layer can be decreased to a roomtemperature while maintaining the colored state, and then the reversiblethermal recording layer becomes the colored state (C) that is a statethat the colored state is stabilized and fixed. This colored state canbe obtained depending on the temperature decreasing speed from themelted state. When the reversible thermal recording layer is cooledslowly, decoloring occurs to the reversible thermal recording layer whenthe temperature is being decreased, and then the reversible thermalrecording layer becomes the decolored (transparent) state (A) same asthe initial state or the reversible thermal recording layer becomes astate having a color density lower than the colored state (C) caused bythe rapid cooling.

When the temperature of the reversible thermal recording layer havingthe colored state (C) is increased again, the decoloring occurs to thereversible thermal recording layer at a temperature T2, which is lowerthan the coloring temperature T1 (i.e., from (D) to (E)). When thetemperature of the reversible thermal recording layer at the decolored(transparent) state (E) is decreased, the reversible thermal recordinglayer returns to the decolored (transparent) state (A), which is theinitial state.

The colored state (C) transformed from the melted state (B) by the rapidcooling corresponds to a state that molecules of the Leuco dye and thedeveloper are mixed with a state that the molecules can contact andreact, which may be a solid state. At the colored state (C), meltinglyblended compound (colored compound) of the Leuco dye and the developeris crystalized and maintains the colored state, and this structure canstabilize the colored state. By contrast, the decolored (transparent)state (A) corresponds to a state that the Leuco dye and the developerare separated. The decolored (transparent) state (A) may occur byaggregation of at least one of the Leuco dye and the developer as adomain or crystallization, in which the Leuco dye and the developer areseparated and stabilized by aggregation or crystallization. Typically,when the Leuco dye and the developer are separated and the developer iscrystallized, the decolored (transparent) state (A) may occur morecompletely.

As indicated in FIG. 17A, both of the decoloring from the melted state(B) by the slower cooling and the decoloring from the colored state (C)by the temperature increase occur at the temperature T2, in which theaggregation structure changes, and the phase separation and thecrystallization of developer occur. Further, in a case of FIG. 17A, ifthe reversible thermal recording layer is repeatedly heated totemperature T3 higher than the melting temperature T1, a failure oferasing that the erasing cannot be completed even if heated may occureven if the reversible thermal recording layer is heated at the erasingtemperature. The failure of erasing may occur due to heat decompositionof the developer, with which the developer is hard to aggregate orcrystallize, and also hard to separate from the Leuco dye. Thedeterioration of the reversible thermal recording medium caused by therepeated use can be suppressed by setting a difference of the meltingtemperature T1 and the temperature T3 (see FIG. 17A) smaller when thereversible thermal recording medium is heated

The above described mechanism of image recording and image erasing canbe applied as follows. Specifically, a temperature threshold can be setfor the reversible thermal recording medium, and the irradiation poweror the irradiation power density is controlled so that the temperaturedoes not exceed the temperature threshold. For example, the temperaturethreshold can be set by two methods. Method (1): the temperature T2 isset as the temperature threshold. The irradiation power or theirradiation power density of laser light is controlled so that themedium temperature (temperature of reversible thermal recording medium)is maintained at the temperature T2 or less that the image recording andthe image erasing does not occur. Method (2): the temperature T1 is setas the temperature threshold when the image recording is performed, andthe temperature T2 is set as the temperature threshold when the imageerasing is performed. The irradiation power or the irradiation powerdensity of laser light is controlled so that the medium temperature(temperature of reversible thermal recording medium) does not exceedsthe temperature threshold for both of the Methods (1) and (2).

The minimum energy (minimum value) of the irradiation power that themedium temperature (temperature of reversible thermal recording medium)does not exceeds the temperature threshold can be set in view ofprocess-target objects and purposes. The minimum energy of theirradiation power can be determined experimentally based on, forexample, image quality of bar code, sensual inspection, and surfacechange, deformation and smelting of processing material used forprocessing use without measuring the temperature threshold. Thisdetermination method can be used to allow a very small “structuraltransformation” that cannot be recognized clearly.

Further, the temperature threshold varies depending on temperatureproperties of each of components such as medium temperature and thelight source temperature. The temperature threshold can be effectivelycorrected based on a measurement value detected by a temperature sensorused for detecting the medium temperature and the light sourcetemperature. For example, the correction unit can set I-L temperatureproperty (temperature property for current to light output) of the laserlight as a temperature profile. The outputting peak power can beestimated based on the acquired temperature of light source, and thepower can be adjusted by correcting the pulse width, with which themedium temperature can be controlled.

A description is given of the irradiation method of laser light of thelight irradiation apparatus 100 of the first example embodiment withreference to FIG. 8. FIG. 8 is a flowchart illustrating the steps ofprocesses performable by the main controller 50 a based on a processingalgorithm. The control is started when a user inputs a request forstarting the processing to the information rewritable system such as therewritable laser system by using a touch panel of a monitor unit, andthen the request is received by the main controller 50 a. The monitorunit and the main controller 50 a are communicably connected with eachother.

The laser light irradiation mode can be set by the user's operation ofthe touch panel. Specifically, the laser light irradiation mode can beset to any one of the recording mode and the erasing mode as the initialsetting. In this example configuration, the erasing mode is set as theinitial setting, in which the erasing mode is performed as the beginningprocess and then the erasing mode and the recording mode can berepeatedly performed alternately.

Specifically, labels made of reversible thermal recording medium andattached to transport-use containers conveyable one by one at a positionfacing the light irradiation apparatus 100 by the transport unit such asa conveyor belt are recorded with images to be erased. After erasing therecorded images by using the light irradiation apparatus 100, new imagescan be recorded on the labels. The image erasing and image recordingoperation can be repeatedly performed for each one of the transport-usecontainers.

For example, the main controller 50 a sets the light output level “PL”matched to the image recording when the recording mode is set, and thelight output level “PH” matched to the image erasing when the erasingmode is set.

Further, the main controller 50 a sets the diffusing lens 16 at a focusposition that can generate a beam spot diameter matched to the imagerecording when the recording mode is set, and sets the diffusing lens 16at a de-focus position that can generate a beam spot diameter matched tothe image erasing when the erasing mode is set (hereinafter, de-focusposition for erasing).

With this configuration, when the recording mode is set, the irradiationpower density such as Dth or more corresponding to a combination of thelight output level “P_(H)” and focus position can be generated on therecording medium, and thereby an image can be recorded or formed on therecording medium with a good precision. Further, when the erasing modeis set, the irradiation power density such as Dth or more correspondingto a combination of the light output level “P_(L)” and the de-focusposition for erasing can be generated on the recording medium, andthereby an image on the recording medium can be erased with a goodprecision.

At step S1, it is determined whether a mode change timing has come.Specifically, it is determined whether the erasing mode or the recordingmode is completed Step S1 can be performed by monitoring the lightemission operation of the LD for each of the modes based on the lightemission control signal by using the main controller 50 a as a monitor.If it is determined that the mode change timing has not come (S1: NO),the sequence becomes a “standby mode.” If it is determined that the modechange timing has come (S1: YES), the sequence proceeds to step S2.

At step S2, the diffusing lens 16 positioned at the position beforechanging the mode (e.g., focus position or the de-focus position forerasing) is moved to a position where the beam spot diameter on therecording medium can be set effectively greater than the beam spotdiameter when the image recording is performed and the beam spotdiameter when the image erasing is performed. In another words, thediffusing lens 16 is moved to another de-focus position having ade-focus level effectively greater than a de-focus level used for thede-focus position for erasing, which means that the diffusing lens 16 ismoved to a position where the irradiation power density of the beam spotdiameter on the recording medium becomes smaller than the minimumirradiation power density Dth.

With employing this configuration, the irradiation power density of thebeam spot on the recording medium can be set to a value that thestructural transformation of the recording medium does not occur duringthe transition time period “Ts” corresponding to mode changing period,and thereby image forming failure and image erasing failure can besuppressed.

At step S3, it is determined whether a given time has elapsed. The giventime is set with a value greater than the transition time period “Ts.”For example, the given time is set with a value slightly greater thanthe transition time period “Ts” to enhance the through-put of the systemoperation (i.e., to reduce the time loss of system operation). If it isdetermined that the given time has not elapsed (S3: NO), the sequencebecomes a time-waiting status, and if it is determined that the giventime has elapsed (S3: YES), the sequence proceeds to step S4.

At step S4, the diffusing lens 16 is moved to a position after changingthe mode (e.g., focus position or de-focus position for erasing).

At step S5, it is determined whether the processing is completed. If itis determined that the sequence is to be continued (S5: NO), thesequence returns to step S1, and if it is determined that the sequenceis completed (S5: YES), the sequence is completed.

In addition to the mode change timing, the processes of FIG. 8 can bepreferably performed, for example, when the light output level isincreased from zero when the process is to be started, or when the lightoutput level is decreased to zero when the process is to be completed.When the light output level is increased from zero, the position of thediffusing lens 16 before changing the light output level (when the lightoutput level is 0) can be set at any positions. Further, when the lightoutput level is decreased to zero, the position of the diffusing lens 16after changing the light output level (when the light output level is 0)can be set at any positions.

The above described light irradiation apparatus 100 of the first exampleembodiment includes the irradiation unit such as the light source unit11 employing, for example, a laser diode (LD) as a light source thatirradiates the laser light onto the recording medium (i.e.,process-target object), the light source drive circuit 50 b that drivesthe LD, the main controller 50 a that changes the light output level ofthe LD by using the light source drive circuit 50 b, an irradiationpower density controller (light spot controller) that controls theirradiation power density (energy density) of the beam spot on therecording medium, in which the light output level during the mode changetiming is controlled lower than at least one of the light output levelbefore changing the light output level and the light output level afterchanging the light output level.

The change of light output level means, for example, changing the lightoutput level from one value greater than zero to another value greaterthan zero, changing the light output level from zero to one valuegreater than zero, and changing the light output level from one valuegreater than zero to zero.

As to the light irradiation apparatus 100 of the first exampleembodiment, the energy density of beam spot on the process-target objectcan be set to a value that the structural transformation of therecording medium may not occur during the time of changing the lightoutput level (i.e., transition time of light output level). Thestructural transformation of the reversible thermal recording mediummeans, for example, a transformation of phases between the recordingmode and the erasing mode, and the structural transformation of theprocessing material means, for example, smelting and shape change of theprocessing material.

With employing this configuration, the occurrence of unintendedstructural transformation of the recording medium can be suppressed.

By contrast, when conventional LED driving circuits are employed for alight irradiation apparatus, the transition time period of severalmilliseconds (ms) to several tens milliseconds (ms) is required tostabilize the light output level even if the light output level ischanged by using the LED driving circuit, in which the energy (e.g.,heat, light) irradiated to the process-target object during thetransition time period may cause the unintended structuraltransformation on the process-target object depending on the energydensity.

Further, the irradiation power density controller of the first exampleembodiment can further include the diffusing lens 16 disposed on thelight path of light emitted from the LD. Therefore, the irradiationpower density of the beam spot on the process-target object can becontrolled by a simple method such as adjusting the focus position ofthe diffusing lens 16.

Further, the irradiation power density controller of the first exampleembodiment can further include the focus position control unit 40 thatcan move the diffusing lens 16 along the light-axis direction.Therefore, the irradiation power density of the beam spot on theprocess-target object can be controlled by a simple method such as usingthe focus position control unit 40.

Further, the irradiation power density controller can further includethe lens driver 17 as the focus position control unit 40 to drive thediffusing lens 16, which is used for adjusting the focus position of theoptical unit 30 between the recording mode and the erasing mode.Therefore, compared to a configuration using a special device to controlthe irradiation power density, the number of parts can be reduced, thecost of the apparatus can be set lower, and the size of the apparatuscan be reduced.

In another viewpoint, the irradiation unit can further include theoptical unit 30 disposed on the light path of the light emitted from theLD, and the irradiation power density controller can adjust the focusposition of the diffusing lens 16 of the optical unit 30.

With employing this configuration, the irradiation power density of thebeam spot on the process-target object can be controlled by a simpleconfiguration.

Further, when the light output level is being changed, the irradiationpower density controller can control the energy density of beam spotformed on the recording medium with reference to a minimum value thatcause the structural transformation on the recording medium such as theminimum irradiation power density Dth, with which the irradiation oflight having the unstable output level that causes unintended structuraltransformation on the recording medium can be suppressed effectively.

Further, the light source drive circuit 50 b includes, for example, theLC filter composed of the coil L and the capacitor C, the DC powersource electrically connectable with the LC filter, the switchingelement SW1 that switches electrical conduction and non-conductionbetween the LD and the LC filter, the light emission controller 107 thatcontrols the switching element SW1 based on the light output level,including the current sensor 102, the current detector 103 and thecurrent controller 104 that controls the drive current I_(LD) appliedfrom the DC power source to the LD via the LC filter based on the setcurrent value (threshold “Ith”) of the light output level.

With employing this configuration, the drive current I_(LD) can bestabilized at a value close to the desired current value, and therebythe light output level of the LD can be stabilized at a value close tothe desired light output level. Further, for example, compared to aconventional configuration using the L filter alone, the size reductionand lower cost can be achieved.

Further, since the main controller 50 a can change the light outputlevel of the LD between the first light output level (P_(L)) used forthe image recording on the recording medium and the second light outputlevel (P_(H)) used for the image erasing on the recording medium, onelight irradiation apparatus 100 can perform both of the image recordingand the image erasing onto the recording medium.

Further, the main controller 50 a can change the light output levelbetween one of the first and second the light output levels and zero.For example, when the process is to be started, the light output levelcan be increased from zero to one of the first and second the lightoutput levels for performing the image recording or the image erasing,and when the process is to be completed, the light output level can bedecreased from one of the first and second the light output level tozero.

Further, the information rewritable system such as the rewritable lasersystem can include the light irradiation apparatus 100, and thetransport unit that transports the transport-use containers (objects)attached with the recording medium on a conveying path or route facingthe light irradiation apparatus 100. Therefore, the image recording andthe image erasing can be repeatedly performed for each one of thetransport-use containers being conveyed on the conveying pathconsecutively with higher precision.

As to the first example embodiment, when the light output level is to bechanged, the beam spot diameter is set with a value so that theirradiation power density of the beam spot generated on the reversiblethermal recording medium during the transition time period “Ts” forstabilizing the light output level becomes effectively smaller than theminimum irradiation power density Dth required for the “structuraltransformation” such as the image erasing or the image recording on thereversible thermal recording medium.

Further, the unintended structural transformation of the recordingmedium can be suppressed by setting the irradiation power (energy,energy density) of the beam spot on the recording medium effectivelysmaller than the minimum irradiation power density required for the“structural transformation” on the reversible thermal recording mediumduring the transition time period “Ts.” For example, the unintendedstructural transformation of the recording medium can be suppressed byblocking a part of the irradiation light. Hereinafter, a description isgiven of a light irradiation apparatus that can block a part of theirradiation light

SECOND EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 200 of a secondexample embodiment with reference to FIGS. 9 and 10. As illustrated inFIG. 9, the light irradiation apparatus 200 includes, for example, anaperture member 10 at a position on a light path of laser lightextending from the light source unit 11 to the recording medium.Specifically, the aperture member 10 can employ an aperture stop thatcan adjust an aperture size such as aperture diameter at a position onthe light path of laser light extending from the light source unit 11 tothe recording medium, in which the aperture member 10 can be used as alight shielding member that can block the laser light. The lightirradiation apparatus 200 includes the control system 50 having anaperture diameter controller. Further, instead of the irradiation powerdensity controller, the light irradiation apparatus 200 can include anirradiation power controller.

The configuration of the light irradiation apparatus 200 can be compactin size compared to a configuration that a lens of a lens system isdriven and moved mechanically.

Specifically, as illustrated in FIG. 10, the aperture member 10 canemploy an aperture stop having a plurality of diaphragm blades that canbe controlled by the aperture diameter controller. When the aperturediameter of the aperture member 10 is adjusted by the aperture diametercontroller, a part of the light that is directing from the light sourceunit 11 to the recording medium can be blocked, and thereby theirradiation power on the recording medium can be controlled. Forexample, when the aperture diameter of the aperture stop is set to amaximum diameter, the incident light that enters the aperture member 10can pass through the entire of incident light, and when the aperturediameter of the aperture stop is set to a minimum diameter such as zero(0), the aperture member 10 can block the entire of incident light. Thespecification of aperture stop (e.g., adjustment width, maximumdiameter, minimum diameter of aperture diameter) can be designed andchanged as required.

In this description, the aperture member 10 is disposed on the lightpath of the laser light between the condensing lens 18 and the lightscanning unit 13, but not limited hereto. For example, the aperturemember 10 can be disposed on the light path at a position between thelight source unit 11 and the collimator lens 12 b, at a position betweenthe collimator lens 12 b and the diffusing lens 16, at a positionbetween the diffusing lens 16 and the condensing lens 18, or at aposition between the light scanning unit 13 and the exit window 15 w.

Further, the light shielding member is not limited to the aperturemember 10, but any members that can block at least a part of laser lighton the light path and can adjust the light blocking amount can beemployed. For example, a diffusion plate or a light-heat converter 20,to be described later, can be disposed at a position so that thediffusion plate or a light-heat converter 20 can be moved to cross thelight path of laser light as required.

The aperture diameter controller is operated to control the aperturediameter of the aperture member 10 at a smaller size when the lightoutput level is being changed compared to the aperture diameter beforeand after the light output level is changed. For example, when the lightoutput level is being changed, the aperture diameter of the aperturemember 10 is changed to a size that can pass through a part of the laserlight, and before or after the light output level is changed, theaperture diameter of the aperture member 10 is changed to a size thatcan pass through the entire of laser light.

The irradiation method of laser light using the light irradiationapparatus 200 of the second example embodiment can be performed similarto the irradiation method of FIG. 8. Further, in addition to the modechange timing, the process indicated in FIG. 8 is performed preferablywhen the light output level is increased from zero when the process isto be started, and when the light output level is decreased to zero whenthe process is to be completed. When the light output level is increasedfrom zero, the aperture diameter of the aperture member 10 before themode changing (i.e., the light output level is 0) can be set any size.Further, when the light output level is decreased to zero, the aperturediameter of the aperture member 10 after the mode changing (i.e., thelight output level is 0) can be set any size.

The light irradiation apparatus 200 of the second example embodimentincludes, the irradiation power controller such as the light shieldingmember that can adjust the light blocking amount of the light emittedfrom LD partially or entirely, with which the light irradiationapparatus 200 of the second example embodiment can attain the effectsimilar to the first example embodiment, and can control the irradiationpower of the beam spot on the recording medium with a simple method.

Further, the light irradiation apparatus 200 of the second exampleembodiment can employ the light shielding member using the aperture stopthat can adjust the aperture diameter. Therefore, the irradiation powerof the beam spot of on the recording medium can be controlled with asimple method even if the light output level of the laser light isunstable.

THIRD EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 300 of a thirdexample embodiment with reference to FIGS. 11 and 12.

Different from the light irradiation apparatus 100 of the first exampleembodiment, the light irradiation apparatus 300 of the third exampleembodiment includes, for example, an optical deflector 14 and alight-heat converter 20 as illustrated in FIG. 11. Specifically, asillustrated in FIG. 11, the optical deflector 14 is disposed at aposition on the light path of laser light between the collimator lens 12b and the diffusing lens 16, and the light-heat converter 20 is disposedat a position deviated from the light path of laser light extending fromthe light source unit 11 to the recording medium. The light-heatconverter 20 can be used as one example of the light shielding member.In this description, the light shielding member means a first memberdisposed at any positions along the light path of laser light extendingfrom the light source unit 11 to the recording medium so that the lightpath of laser light to the recording medium can be blocked at leastpartially by the first member as required, or a second member disposedat any positions deviated from the light path of laser light extendingfrom the light source unit 11 to the recording medium to guide the laserlight to the second member as required so that the laser light is notused to irradiate the recording medium.

(Optical deflector)

The optical deflector 14 can employ, for example, optical deflectiveelements such as acousto-optical device (e.g., acousto-optical lens(AOL)), a galvano scanner and a MEMS scanner, and can deflect the laserlight with high speed such as a deflection cycle of several milliseconds(ms) or less.

(Light-heat converter)

The light-heat converter 20 is made of material that can absorb lightenergy of laser light. For example, the light-heat converter 20 is madeof a substance (e.g., metal, resin, paper) coated with light-heatconverting material, and the surface processed by electrostatic flockingto reduce the surface reflection rate of the laser light.

In the third example embodiment, the light-heat converter 20 is disposedinside the casing 15 of the light irradiation apparatus 300 (see FIG.11). When the light-heat converter 20 is disposed inside the casing 15,the parallel light coming from the collimator lens 12 b is deflected by,for example, the acousto-optical lens (AOL), the galvano scanner and theMEMS scanner with a high speed such as an deflection cycle of severalmilliseconds (ms) or less to direct the parallel light to the light-heatconverter 20. The optical deflector 14 and the light-heat converter 20can be collectively used as the light shielding member.

As to the light irradiation apparatus 300, the laser light emitted fromthe light source unit 11 becomes the parallel light by the collimatorlens 12 b, and then enters the optical deflector 14. The opticaldeflector 14 is disposed to switchingly direct the parallel light comingfrom the collimator lens 12 b to a direction to the diffusing lens 16(i.e. direction guiding the light to the recording medium) or adirection to the light-heat converter 20. The optical deflector 14 canbe controlled by the main controller 50 a .

In this configuration, the main controller 50 a (see FIG. 3) controlsthe optical deflector 14 to deflect the parallel light coming from thecollimator lens 12 b to the diffusing lens 16 at least before and afterchanging the light output level of the LD. The light diffused by thediffusing lens 16 is condensed by the condensing lens 18, and thenscanned on the recording medium by the light scanning unit 13.

By contrast, the main controller 50 a controls the optical deflector 14to deflect the parallel light to the light-heat converter 20 when thelight output level of the LD is being changed (i.e., during thetransition time period).

With this configuration, the laser light having the desired stabilizedoutput level can be irradiated onto the recording medium.

A description is given of the irradiation method of laser light of thelight irradiation apparatus 300 of the third example embodiment withreference to FIG. 12. FIG. 12 is a flowchart illustrating the steps ofprocesses performable by the main controller 50 a based on a processingalgorithm. The processes of FIG. 12 can be performed similar to theprocesses of FIG. 8. Initially, a travelling direction (i.e., deflectiondirection) of laser light by the optical deflector 14 may be set to adirection guiding the laser light to the recording medium.

At step S11, it is determined whether a mode change timing has come. Ifit is determined that the mode change timing has not come (S11: NO), thesequence repeats step S11, and if it is determined that the mode changetiming has come (S11: YES), the sequence proceeds to step S2.

At step S12, the travelling direction of the laser light emitted fromthe LD is changed from the direction to the recording medium to thedirection to the light-heat converter 20.

With this configuration, the irradiation of light having the unstablelight output level that may cause the unintended structuraltransformation on the recording medium during the transition time period“Ts” (i.e., mode is being changed) can be suppressed, and thereby imageforming failure and image erasing failure can be suppressed.

At step S13, it is determined whether a given time has elapsed. Thegiven time is set with a value greater than the transition time period“Ts.” For example, the given time is set with a value slightly greaterthan the transition time period “Ts” to enhance the through-put of thesystem operation (i.e., to reduce the time loss of system operation). Ifit is determined that the given time has not elapsed (S13: NO), thesequence repeats step S13, and if it is determined that the given timehas elapsed (S13: YES), the sequence proceeds to step S14.

At step S14, the travelling direction of the laser light emitted fromthe LD is changed from the direction to the light-heat converter 20 tothe direction to the recording medium.

At step S15, it is determined whether the sequence is completed. If itis determined that the sequence is to be continued (S15: NO), thesequence returns to step S11, and if it is determined that the sequenceis completed (S15: YES), the sequence is completed.

In addition to the mode change timing, the processes of FIG. 12 can bepreferably performed, for example, when the light output level isincreased from zero when the process is to be started, or when the lightoutput level is decreased to zero when the process is to be completed.When the light output level is increased from zero, the deflectiondirection set by the optical deflector 14 before changing the lightoutput level (when the light output level is zero) can be set at anydeflection directions. Further, when the light output level is decreasedto zero, the deflection direction set by the optical deflector 14 afterchanging the light output level (when the light output level is 0) canbe set at any deflection directions.

The above described light irradiation apparatus 300 of the third exampleembodiment includes the irradiation unit such as the light source unit11 employing, for example, the laser diode (LD) as a light source thatirradiates the laser light onto the recording medium (i.e.,process-target object), the light source drive circuit 50 b includingthe LC filter having the coil L and the capacitor C that drives the LD,the main controller 50 a (light source controller) that changes thelight output level of the LD by using the light source drive circuit 50b, a travelling direction controller that controls the travellingdirection of the light emitted from LD so that the laser light is notirradiated onto the recording medium when the light output level isbeing changed.

With employing this configuration, the occurrence of intended structuraltransformation on the recording medium can be suppressed.

Further, the travelling direction controller can include the opticaldeflector 14 that deflects the light emitted from the LD. Therefore, thetravelling direction of light can be switched between the transitionmode (i.e., when the light output level is being changed and one of theoperation modes such as the image writing mode and image erasing mode(i.e., before or after changing the light output level) easily andfaster.

Further, the above described light irradiation apparatus 300 includesthe light-heat converter 20 (light shielding member) at the positiondeviated from the light path of laser light extending from the LD to therecording medium. Since the travelling direction controller can controlthe travelling direction of the laser light to the light shieldingmember when the light output level is being changed, the laser light isnot reflected in the light irradiation apparatus 300 to the direction tothe recording medium when the light output level is being changed.

Further, the light-heat converter 20 can convert a part of the incidentlaser light to heat or diffuse a part of the incident laser light.Therefore, the irradiation of stray light having stronger intensityinside the apparatus can be suppressed.

Further, as to the operational flow of the light irradiation apparatus300, a preliminary irradiation of laser light is preferably performedbefore outputting the laser light when the image recording and the imageerasing is performed by setting the irradiation position of the laserlight to the light-heat converter 20 at a given time. The output patternof the preliminary irradiation can employ a continuous wave (CW) orpulse wave pattern. When the output pattern employs the pulse wavepattern, the average light energy used for the irradiation can bereduced. In this case, even if the light-emission duty of preliminaryirradiation is set lower, the both end voltages of the capacitor C canbe increased, and thereby image forming failure and image erasingfailure can be prevented effectively.

Typically, the current control can be stabilized by the average current.Therefore, the greater the duty difference between a duty beforestarting the irradiation and a duty during the irradiation, the greaterthe fluctuation of the writing-started-timing output, and thereby thecurrent may become unstable. The current output can be effectivelystabilized by using the coil L having smaller capacity and the capacitorC having greater capacity.

Further, if the irradiation operation is performed again within a shorttime period (e.g., several seconds) after one irradiation operationwhile the charge can be maintained in the capacitor C for the short timeperiod, the “image forming failure” and “image erasing failure” can bereduced without performing the preliminary irradiation. However, sincethe charge accumulated in the capacitor C decreases due to the leakcurrent of the switching element SW1, the re-charging by the preliminaryirradiation is required when the irradiation operation is to beperformed again after a given waiting time elapses.

When the laser light irradiation is completed, the light irradiationapparatus 300 stops its operation. To prevent the accidental leaking ofthe laser light from the apparatus, when the light irradiation apparatus300 stops its operation, the deflection direction of laser light is setto the light-heat converter 20, or a light block member such as anaperture and a shutter disposed at the exit window 15 w is closed. Whenthe light irradiation apparatus 300 is being operated continuously, itis checked whether the mode switching is selected at a given timing, andthen the deflection direction of laser light is set to the light-heatconverter 20 and the preliminary irradiation is performed before thelaser light irradiation set for each of the operation modes is performedagain.

FOURTH EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 400 of a fourthexample embodiment with reference to FIG. 13. Different from the lightirradiation apparatus 300 of the third example embodiment, asillustrated in FIG. 13, the travelling direction of the laser lightcoming from the condensing lens 18 can be switched between the directionto the light-heat converter 20 or the direction to the recording mediumby using the light scanning unit 13.

Specifically, as to the fourth example embodiment, the recording mediumand the light-heat converter 20 are disposed at respective positionsthat can be scanned by the light scanning unit 13. The main controller50 a controls the light scanning unit 13 to scan the recording medium byusing the laser light coming from the condensing lens 18 at least beforeor after the light output level of the LD is changed, and to scan thelight-heat converter 20 by using the laser light coming from thecondensing lens 18 when the light output level of the LD is beingchanged.

For example, the recording medium is disposed at the center of thescanning range (the center of scan area), and the light-heat converter20 is disposed at the end of the scanning range (the end of scan area).

As illustrated in FIG. 13, the light scanning unit 13 includes, forexample, two galvano scanners 13 a and 13 b, but not limited hereto. Forexample, the light scanning unit 13 can employ a polygon scanner, whichis a rotatable mirror, which can perform the scanning with a scan anglegreater than a scan angle of galvano mirror, and can constantly scan thelight-heat converter 20 before irradiating the light to the recordingmedium as the preliminary irradiation.

The irradiation method of laser light using the light irradiationapparatus 400 of the fourth example embodiment can be performed similarto the irradiation method of FIG. 12. Further, in addition to the modechange timing, the processes of FIG. 12 can be preferably performed, forexample, when the light output level is increased from zero when theprocess is to be started, or when the light output level is decreased tozero when the process is to be completed. When the light output level isincreased from zero, the deflection direction set by the light scanningunit 13 before changing the light output level (when the light outputlevel is zero) can be set at any deflection directions. Further, whenthe light output level is decreased to zero, the deflection directionset by the light scanning unit 13 after changing the light output level(when the light output level is zero) can be set at any deflectiondirections.

As to the light irradiation apparatus 400 of the fourth exampleembodiment, the travelling direction controller such as the maincontroller 50 a controls the light scanning unit 13 used as a scanner tocontrol the travelling direction of the laser light emitted from the LDused for scanning the recording medium.

Therefore, the light irradiation apparatus 400 of the fourth exampleembodiment can perform the effect similar to the third exampleembodiment without using a special dedicated deflector for controllingthe travelling direction of the laser light, with which the sizereduction and lower cost can be achieved.

FIFTH EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 500 of a fifthexample embodiment with reference to FIG. 14. Different from the fourthexample embodiment, the light-heat converter 20 is disposed outside thecasing 15 of the light irradiation apparatus 500 as illustrated in FIG.14.

The irradiation method of laser light using the light irradiationapparatus 500 of the fifth example embodiment can be performed similarto the fourth example embodiment.

As to the fifth example embodiment, the light scanning unit 13 employs,for example, two galvano scanners 13 a and 13 b. The light-heatconverter 20 can be disposed at any positions. For example, thelight-heat converter 20 can be disposed on the surface of the reversiblethermal recording medium, or a plane including the surface of thereversible thermal recording medium to perform the high speed switchingsuch as several milliseconds (ms) or less.

Since the unintended laser light having unstable output is irradiatedoutside the light irradiation apparatus 500, a configuration that thelight-heat conversion does not affect the reversible thermal recordingmedium is required. For example, a non-effective area having no“structural transformation” can be formed on a part of the reversiblethermal recording medium such as a square of several centimeters withoutcoating the reversible thermal recording layer. As to the fifth exampleembodiment, the laser light is irradiated to the light shielding member20 disposed on the non-effective area, but not limited hereto. Forexample, the laser light can be irradiated directly to the non-effectivearea without disposing the light shielding member 20. When the laserlight can be irradiated directly to the non-effective area, the lightshielding member 20 can be omitted.

As to the light irradiation apparatus 500 of the fifth exampleembodiment, the travelling direction controller such as the maincontroller 50 a controls the light scanning unit 13 to direct thetravelling direction of the laser light to the light shielding member 20disposed on the non-effective area where the structural transformationdoes not occur on the recording medium when the light output level isbeing changed. Therefore, the light irradiation apparatus 500 of thefifth example embodiment can perform the effect similar to the fourthexample embodiment without enlarging the scan area by the light scanningunit 13, with which the size reduction can be achieved.

SIXTH EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 600 of a sixthexample embodiment with reference to FIG. 15. Different from the firstexample embodiment, a shutter 21 is disposed in the casing 15 of thelight irradiation apparatus 600 as illustrated in FIG. 15

Specifically, the shutter 21 is disposed at a position that can block atleast a part of the light path of laser light coming from the lightscanning unit 13. The shutter 21 can be used as the light shieldingmember.

For example, the shutter 21 is disposed near the exit window 15 w of thelight irradiation apparatus 600, but not limited hereto. For example,the shutter 21 can be disposed at any positions near the light path oflaser light extending from the light source unit 11 to the exit window15 w.

The shutter 21 can be moved with respect to the light path of laserlight by using a drive unit including a pulse motor, a liner motor orthe like with a high speed such as several milliseconds (ms) or less.The drive unit can be controlled by the main controller 50 a.

The shutter 21 can employ, for example, a slide shutter, a swing shutteror the like to block the light. Further, the shutter 21 can employ, forexample, an aperture member such as an aperture stop that can adjust theaperture size such as diameter. By employing the aperture stop as theshutter 21, the laser light having the irradiation power density greaterthan the minimum irradiation power density that causes the structuraltransformation of the recording medium can be blocked at leastpartially, and can be blocked completely by closing the aperture.Further, the shutter 21 can be made of the same or similar material ofthe above described light-heat converter 20.

The irradiation method of laser light using the light irradiationapparatus 600 of the sixth example embodiment is described withreference to FIG. 16. FIG. 16 is a flowchart illustrating the steps ofthe irradiation method of laser light using the light irradiationapparatus 600 of the sixth example embodiment. As to the lightirradiation apparatus 600, the shutter 21 can be moved between a lightblock position and a retraction position retractable from the lightblock position. At the light block position, the shutter 21 can block atleast a part of the laser light (i.e., scan light) coming from the lightscanning unit 13, and at the retraction position, the shutter 21 doesnot block the laser light (i.e., scan light) coming from the lightscanning unit 13. Initially, the shutter 21 can be set at the retractionposition.

As to the irradiation method of laser light using the light irradiationapparatus 600 of the sixth example embodiment, after step S21 isperformed, the shutter 21 is moved from the retraction position to thelight block position when the light output level is being changed (stepS22). After the light output level is changed (step S23: YES), theshutter 21 is moved from the light block position to the retractionposition (step S24). Steps S21, S23 and S25 are same as steps S1, S3 andS5 of FIG. 8. Further, when the light output level before or after thetransition mode (i.e., the light output level is being changed) is setzero, the shutter 21 can be set at the light block position.

The light irradiation apparatus 600 of the sixth example embodimentincludes, for example, the irradiation unit such as the light sourceunit 11 employing, for example, the laser diode (LD) as a light sourcethat irradiates the laser light onto the recording medium (i.e.,process-target object), the light source drive circuit 50 b includingthe LC filter having the coil L and the capacitor C that drives the LD,the main controller 50 a (light source controller) that changes thelight output level of the LD by using the light source drive circuit 50b, the shutter 21 that can be moved between the light block position toblock at least a part of the laser light coming from the LD, and theretraction position retractable from the light block position, and aposition controller including the drive unit that moves the shutter 21to the retraction position before or after changing the light outputlevel, and moves the shutter 21 to the light block position when thelight output level is being changed.

In this configuration, the shutter 21 can block at least a part of theunstable laser light that may cause the unintended structuraltransformation on the recording medium when the light output level isbeing changed.

With employing this configuration, the occurrence of unintended“structural transformation” on the recording medium can be suppressed.

SEVENTH EXAMPLE EMBODIMENT

A description is given of a light irradiation apparatus 700 of a seventhexample embodiment with reference to FIGS. 18 and 19. As to the lightirradiation apparatus 700 of the seventh example embodiment, when theimage erasing is performed and when the image recording is performed,the light source (e.g., LD) is modulated to change a peak power (i.e.,light output level) differently.

The time required for the image recording process and the image erasingprocess can be set shorter by increasing the irradiation power of thebeam spot formed on the recording medium, in which the recording mediumsuch as the reversible thermal recording medium can be heated with ashorter time.

For example, when the image erasing is performed, the heatingtemperature for the image erasing can be set lower than the heatingtemperature for the image recording but the heating time for the imageerasing is required to be set longer than the heating time for the imagerecording. Therefore, when the image erasing is performed with a highspeed, the heating time and the heating temperature required for thehigh speed image erasing can be devised by increasing the beam diameterand irradiating the laser light with higher power onto the recordingmedium.

By contrast, when the image recording is performed with a higherprecision and with a higher speed, the beam diameter is required to beset smaller. Therefore, the focus position of the diffusing lens 16 isadjusted at a position close to an irradiation face by the laser lightsuch as the surface of recording medium.

The output control (i.e., modulation) of the light source includes, forexample, a peak power control method such as intensity modulation and apulse width control method such as pulse width modulation (PWM).

FIG. 18 is a schematic graph of an average output (i.e., irradiationlight power) of the light source when the pulse width control method isapplied. As indicated in FIG. 18, the irradiation light power such asthe average light power “Pw” can be defined as “Pw=Pp×D” by using thepeak power “Pp” and the duty ratio of pulse “D=W/T” defined by cycle “T”and pulse width “W.” Therefore, the irradiation light power “Pw” thatcauses the “structural transformation” of the reversible thermalrecording medium can be changed by adjusting at least one of the peakpower “Pp” and the duty ratio “D.”

By contrast, as to the peak power control method, the change of the peakpower “Pp” with a high speed becomes harder to perform as the peak power“Pp” becomes greater. Since the irradiation power is required to bechanged with a high speed when the image recording is performed, thepeak power control method may not be useful.

By contrast, as to the pulse width control method, the high speedcontrol can be performed. However, when the higher peak power is set forperforming the image erasing and the smaller pulse width is set forperforming the image recording, the higher energy is irradiated onto therecording medium within a shorter time, in which the durability of thereversible thermal recording medium over the repeated use maydeteriorate.

Therefore, if the peak power control method alone or the pulse widthcontrol method alone is used, the high speed response and the durabilityof the reversible thermal recording medium over the repeated use cannotbe achieved at the same time.

In view of this issue, as to the light irradiation apparatus 700 of theseventh example embodiment, the irradiation power control employs bothof the peak power control method and the pulse width control method.Specifically, the peak power control method is used to change the peakpower with two steps when the image erasing process and the imagerecording process are switched from one to another, and the pulse widthcontrol method is used for each of the image recording process and theimage erasing process because the output control for each of the imagerecording process and the image erasing process requires the higherspeed power control.

As to the seventh example embodiment, when the peak power is changedduring the transition time period such as when the image erasing processis switched to the image recording process and vice versa, theirradiation of unintended energy not required for the reversible thermalrecording medium can be suppressed, and thereby the unintendedstructural transformation such as image forming failure and imageerasing failure can be suppressed. The transition time period and itseffect caused by the light source driving circuit including a LC filterwhen the peak power is changed can be the same as disclosed withreference to FIGS. 7 and 8

A description is given of a configuration of the main controller 50 a ofthe control system 50 of the seventh example embodiment with referenceto FIG. 19.

As to the seventh example embodiment, as illustrated in FIG. 19, themain controller 50 a includes, for example, a modulator 50 a-1, atemperature sensor 50 a-2, a scan speed detector 50 a-3, a correctionunit 50 a-4 and a light output setting unit 50 a-5.

(Modulator)

The modulator 50 a-1 outputs a modulation signal such as pulse widthmodulation (PWM) signal to the light source such as LD to modulate thelight source directly, with which the irradiation power of the beam spoton the recording medium can be controlled. For example, thelight-emission duty ratio “D=W/T” is changed based on a PWM signal of 40kHz to control the irradiation power. When the image recording processor the image erasing process are performed normally, the light-emissionduty ratio used as a standard duty ratio for the room temperature of 25Celsius degrees is set 75% (hereinafter, also referred to “standard dutyratio”). The light-emission duty ratio can be corrected based on, forexample, temperature of the recording medium, scan speed or the like.(Temperature sensor)

The temperature sensor 50 a-2 is used to detect and acquire temperatureof the process-target object. When the temperature sensor 50 a-2measures temperature of the reversible thermal recording mediumindirectly such as without contacting, the temperature sensor 50 a-2employs a thermistor to measure ambient temperature of the reversiblethermal recording medium. Further, the temperature sensor 50 a-2 is notlimited to the thermistor, but the temperature sensor 50 a-2 can employa contact type temperature sensor such as thermocouple and resistancetemperature detector (RTD), and a non-contact type temperature sensorsuch as radiation thermometer.

(Scan speed detector)

The scan speed detector 50 a-3 is used to detect and acquire the scanspeed of laser light on a scan target face on the reversible thermalrecording medium. The scan speed of laser light can be acquired usingany methods. For example, the scan speed of laser light can becalculated from the rotation speed of a scan mirror and the distancebetween the scan mirror and the process-target object, which is thedistance to work.

(Correction unit)

The correction unit 50 a-4 is used to correct the light-emission dutyratio of PWM signal output from the modulator 50 a-1 based on therecording medium temperature acquired by the temperature sensor 50 a-2and the scan speed of laser light acquired by the scan speed detector 50a-3. The irradiation power matched to the reversible thermal recordingmedium becomes greater as the recording medium temperature becomes lowerand the scan speed becomes faster. The light-emission duty ratio can becorrected by, for example, a pulse width correction method executing aprogram by using a computer. Further, the correction unit 50 a-4 cancorrect the light-emission duty ratio based on ambient moisture of therecording medium acquired by a moisture sensor, or based on acombination of the recording medium temperature, the scan speed and themoisture of the recording medium.

(Light output setting unit)

The light output setting unit 50 a-5 is used to set the peak power(i.e., light output level) of the laser light by using the light sourcedrive circuit 50 b. The peak power can be set by auto current control(ACC) and auto power control (APC). As to the ACC, a feedback control isperformed to analog signals including peak information and the drivecurrent of the light source that follows the analog signals. As to theAPC, a feedback control is performed to the output of LD by using aphotodiode. As to the seventh example embodiment, the setting values ofthe peak power can be switched for the image recording process and theimage erasing process.

A description is given of a process of controlling the irradiation power(energy) or the irradiation power density (energy density) by the maincontroller 50 a of the seventh example embodiment with reference toFIGS. 20, 21 and 23. FIGS. 20, 21 and 23 are flowcharts illustrating thesteps of controlling the irradiation power or the irradiation powerdensity by the main controller 50 a. Hereinafter, a mode for controllingthe irradiation power or the irradiation power density is referred to a“base mode,” a mode for controlling the light-emission duty ratio alonefor the base mode is referred to a “lower duty ratio mode,” a mode forcontrolling the scan speed alone for the base mode is referred to a“swing mode,” and a mode for controlling the light-emission duty ratioand the scan speed is referred to a “combined mode (lower duty ratiomode+swing mode).”

FIG. 20 is a flowchart illustrating the steps of a process ofcontrolling the irradiation power or the irradiation power density whenthe lower duty ratio mode is selected. When this sequence starts, thelight irradiation apparatus is already activated, and the initialsetting is completed, and thereby the light irradiation apparatus is inthe state that is ready to irradiate the laser light. As to the initialsetting, the light-emission duty ratio is set to the standard dutyratio.

At step S31, it is determined whether the mode change timing has come.Specifically, the operation modes include, for example, three types ofmodes such as an image recordings mode, an image erasing mode and astandby mode for the reversible thermal recording medium, and the modescan be changed between the modes. If it is determined that the modechange timing has come (S31: YES), the sequence proceeds to step S32,and if it is determined that the mode change timing has not come (S31:NO), the sequence repeats step S31.

For example, when the mode is changed from the standby mode to the imagerecording mode, step S32 is performed to set a lower level for theirradiation power or the irradiation power density during the transitiontime period defined by a time point when the irradiation of laser lightis started and a time point when the peak power of irradiation light isstabilized. Further, for example, when the mode is changed from theimage recording mode to the standby mode, step S32 is performed to set alower level for the irradiation power or the irradiation power densityduring the transition time period defined by a time point when theirradiation of laser light is completed and a time point when the peakpower of irradiation light is stabilized. Further, for example, when themode is changed between the image recording mode and the image erasingmode, step S32 is performed to set a lower level for the irradiationpower or the irradiation power density during the transition time periodfrom the image recording mode to the image erasing mode, or from theimage erasing mode to the image recording mode. However, even if theimage recording is being performed, if an area not formed with image islarger and the time interval of irradiating laser light is longer (e.g..similar to the response speed of the transition time period such asmilliseconds), it is assumed as the mode change timing has come, andstep S32 is performed to fill the time interval of irradiating laserlight.

A situation that is not the mode change timing means a period during thestandby mode, a period during the image recording mode, and a periodduring the image erasing mode.

At step S32, the light-emission duty ratio is decreased from thestandard duty ratio during the mode changing. Specifically, themodulator 50 a-1 sets and performs the lower duty ratio mode during themode changing that the peak power of irradiation light is not yetstabilized (see FIG. 22A). The irradiation light power can be set lowerby setting the lower duty ratio mode, and thereby the temperatureincrease of the reversible thermal recording medium can be suppressed.The lower duty ratio mode is being performed until the peak power isstabilized. The next step S33 determines the execution time of the lowerduty ratio mode.

At step S33, it is determined whether a given time has elapsed. If it isdetermined that given time has elapsed (S33: YES), the sequence proceedsto step S34, and if it is determined that the given time has not elapsed(S33: NO), the sequence repeats step S33. Specifically, the executiontime of the lower duty ratio mode is determined, and then the apparatusis set in a state of executing the execution time of the lower dutyratio mode (i.e. from the start to the end of the lower duty ratiomode). This execution time corresponds to a time period that the peakpower of laser light becomes a desired power such as Pp1 and Pp2 in FIG.22A, and then the peak power of laser light is stabilized. The executiontime is set longer than the transition time period of the peak powersuch as the transition time period having the rising period or thetransition time period having the falling period. For example, theexecution time is set longer for 10 to 90% of the time period from thestart and the end of the rising period, or the execution time is setlonger for 10 to 90% of the time period from the start and the end ofthe falling period. Further, by monitoring the peak power using a lightreceiving element such as photodiode, the time point when the valueexceeds the pre-set value can be set as the execution time.

At step S34, the light-emission duty ratio is returned to the standardduty ratio, in which the lower duty ratio mode is completed, and thelight-emission duty ratio of the normal operation mode is set. Step S34is performed right after step S33 so that the peak power does notfluctuate due to the delay of execution. Specifically, step S34 isperformed after step S33 before a time shorter than the transition timeperiod of the peak power (e.g., the rising period or the falling periodof the peak power) elapses.

At step S35, it is determined whether the processing is completed. Ifthe light irradiation apparatus is still irradiating the laser light orwaiting to complete the operation, it is determined that sequence is notyet completed (S35: NO), and the sequence returns to step S31. If it isdetermined that the image recording or the image erasing is completed(S35: YES), the sequence is completed.

At the end step, the process completion is performed. When theprocessing is completed, the light source drive circuit 50 b isdeactivated to prevent the irradiation of laser light. For example, thelight irradiation apparatus is deactivated by setting a configuration tocovered the exit window 15 w by the shutter to prevent a leak of laserlight to the outside of the apparatus.

FIG. 21 is a flowchart illustrating the steps of a process ofcontrolling the irradiation power or the irradiation power density whenthe swing mode is selected. The processes of steps S41, S43, S45 and endstep of FIG. 21 are respectively similar to the processes of steps S31,S33, S35 and end step of FIG. 20. Therefore, step S42 is described.

At step S42, when the peak power of the irradiation light is not stable,the main controller 50 a sets and performs the swing mode set with afaster scan speed (see FIG. 22B) by using the light scanning unit 13.Since the laser light can be diffused on the recording medium by settingthe swing mode, the irradiation power can be reduced, and thereby thetemperature increase of the reversible thermal recording medium can besuppressed. The above described relationship of the irradiation powerand the scan speed is also applied. The swing mode is performed untilthe peak power is stabilized, and the execution time of the swing modeis determined at next step S43. If it is determined that given executiontime has elapsed (S43: YES), the sequence proceeds to step S44. At stepS44, the scan speed is returned to the normal speed.

FIG. 23 is a flowchart illustrating the steps of a process ofcontrolling the irradiation power or the irradiation power density whenthe combined mode of “lower duty ratio mode+swing mode” is selected asthe operation mode of the modulator 50 a-1. The combined mode of “lowerduty ratio mode+swing mode” is a combination of the lower duty ratiomode and the swing mode. Therefore, step S51 corresponding to steps S31and S41, step S52 corresponding to step S32, step S53 corresponding tostep S42, step S54 corresponding to steps S33 and S43, step S55corresponding to step S34, step S56 corresponding to step S44, and stepS51 corresponding to steps S35 and S45 are performed.

By performing the above described processes of any one of FIGS. 20, 21and 23, the irradiation power “k▪Pw/V” (k: factor of proportionality)can be reduced effectively during the mode changing (transition timeperiod) that the peak power of laser light is not yet stabilized.

As described above, the pulse width control method can be performedfaster than the peak power control method as the irradiation powercontrol method.

If the light source drive circuit employs a switching circuit includingthe LC filter as the output filter, the rising time of output currentdetermined by frequency response of the LC filter becomes severalmilliseconds (ms) or more when the peak power control is performed.Further, since the switching circuit performs the current control basedon the average value of output current, the laser light is required tobe irradiated during the peak power control.

If the laser light is being irradiated continuously, the irradiationpower of laser light applies unnecessary energy to the reversiblethermal recording medium when the switching between the image recordingand the image erasing is performed such as during the transition timeperiod of several milliseconds (ms) set for changing the peak power.

As illustrated in FIG. 22A, by decreasing the light-emission duty ratioD from “D_(N)” to “D_(P)” during the transition time period such asseveral milliseconds (ms) set for changing the peak power from “Pp1” to“Pp2,” the irradiation power “k▪Pw/V” can be decreased, with which thetemperature increase of the reversible thermal recording medium can besuppressed.

Further, as illustrated in FIG. 22B, by increasing the scan speed from“V_(N)” to “V_(P)” during the transition time period such as severalmilliseconds (ms) set for changing the peak power from “Pp1” to “Pp2,”the irradiation power “k▪Pw/V” can be decreased, with which thetemperature increase of the reversible thermal recording medium can besuppressed.

As above described, the irradiation power “k▪Pw/V” can be controlled toa value that the temperature of the reversible thermal recording mediumduring the transition time period becomes less than a temperature thatcauses the structural transformation of the reversible thermal recordingmedium by adjusting at least any one of the light-emission duty ratioand the scan speed.

As to the light irradiation apparatus of the seventh example embodiment,the light spot controller includes the modulator 50 a-1 that can changethe light-emission duty ratio of laser light irradiated onto therecording medium.

In this configuration, the beam spot energy (irradiation power) or theenergy density (irradiation power density) generated on the recordingmedium can be set smaller than a minimum value that causes thestructural transformation of the recording medium. Therefore, imageforming failure and image erasing failure causable by the irradiationlight being emitted when the light output level is being changed can besuppressed

The light spot controller can control the irradiation power or theirradiation power density by using the modulator 50 a-1.

Further, the irradiation unit includes the light scanning unit 13 thatscans the laser light, and the light scanning unit 13 can be configuredto change the scan speed of laser light.

In this configuration, the light spot controller can control theirradiation power or the irradiation power density by using the lightscanning unit 13.

Further, the light spot controller can control the irradiation power orthe irradiation power density based on temperature of the recordingmedium.

Further, as to the seventh example embodiment, the main controller 50 ais not required to include the scan speed detector 50 a-3. In this case,the correction unit 50 a-4 corrects the light-emission duty ratio of PWMsignals output from the modulator 50 a-1 by using the recording mediumtemperature received from the temperature sensor 50 a-2.

Further, as to the seventh example embodiment, the main controller 50 ais not required to include the temperature sensor 50 a-2. In this case,the correction unit 50 a-4 corrects the light-emission duty ratio of PWMsignals output from the modulator 50 a-1 by using the scan speed oflaser light received from the scan speed detector 50 a-3.

Further, as to the seventh example embodiment, the main controller 50 ais not required to include the light output setting unit 50 a-5.

Further, as to the seventh example embodiment, the main controller 50 ais not required to include the scan speed detector 50 a-3, thetemperature sensor 50 a-2 and the correction unit 50 a-4. In this case,the modulator 50 a-1 outputs PWM signals to the light source drivecircuit 50 b directly.

As to the above described each one of the example embodiments of thelight irradiation apparatus and the irradiation method of laser light,“image erasing failure” when the image erasing is just started and“image forming failure” when the image recording is just started on thereversible thermal recording medium can be suppressed.

As to the above described each one of the example embodiments of thelight irradiation apparatus, the image processing such as imagerewriting can be performed by the high speed and high precision by usingone light irradiation apparatus.

The configurations of the above described each one of the exampleembodiments of the light irradiation apparatus are just examples, andthe configurations of the light irradiation apparatus can be changedwithin the scope of this specification. For example, the types, numbersand layouts of optical parts in the optical system disposed on the lightpath of laser light emitted from the light source can be changed asrequired.

Further, as to the above described each one of the example embodiments,one light irradiation apparatus is used, but not limited hereto. Forexample, a plurality of light irradiation apparatuses can be arrangedalong the conveying path or route of the transport unit, and then eachof light irradiation apparatuses can be activated one by one orconcurrently.

Further, the configuration of the light source drive circuit can bechanged as required. For example, the light source drive circuit canemploy the L filter instead of the LC filter as required. Further, thelight source drive circuit is not required to include the capacitor Cand the coil L.

Further, the process-target object irradiated by the laser light of thelight irradiation apparatus is not limited to the reversible thermalrecording medium.

A description is given of a background of conceiving the above describedexample embodiments. Conventionally, the image recording and the imageerasing for the reversible thermal recording medium are performed bycontacting a heating source on a reversible thermal recording medium,with which an image is recorded on the reversible thermal recordingmedium. Typically, the heating source employs a thermal head for theimage recording, and a heat roller and ceramic heater for the imageerasing. When the reversible thermal recording medium is flexible membersuch as film, paper, the reversible thermal recording medium can bepressed against the heating source evenly by using a platen to performthe image recording and the image erasing. Further, the image recordingapparatus and the image erasing apparatus can be manufactured with alower cost by using parts used for conventional printers used for theimage recording and the image erasing on heat sensitive paper.

By contrast, some users desire to perform the image writing on thereversible thermal recording medium from a position distanced from theheating source. For example, the image recording and the image erasingcan be performed to the reversible thermal recording medium havingconvex and concave portions by heating the reversible thermal recordingmedium using the heating source distanced from the reversible thermalrecording medium. This method employs a non-contact method for the imagerecording and the image erasing to the reversible thermal recordingmedium attached to transport-use containers used for the logistics line,in which the writing is performed by using laser light, and the erasingis performed by using hot air, hot water or infrared heater.

A laser recording apparatus such as a laser maker can be used for theimage recording and the image erasing to the reversible thermalrecording medium, in which high-powered laser light is irradiated on thereversible thermal recording medium while controlling the position ofthe laser light. Specifically, the laser maker irradiates laser light tothe reversible thermal recording medium. The light-heat convertingmaterial included in the reversible thermal recording medium absorbs thelight and converts the light to heat. The heart can be used for theimage recording and the image erasing. As to the image recording and theimage erasing using laser light, mixture of Leuco dye, reversibledeveloper, and various light-heat converting materials and near infraredlaser light can be used for recording images.

Recently, the lower cost and the size-reduction are demanded for thelight irradiation apparatuses, and a method of irradiating laser byusing one light irradiation apparatus (one light source unit) forperforming both of the image erasing and the image recording isproposed. In this case, the same laser element, and the same lightsource drive unit that drives the laser element are required for theimage erasing and the image recording. The image erasing is performed tothe reversible thermal recording medium by using relatively lowerirradiation power density D_(L), and the image recording is performed tothe reversible thermal recording medium by relatively higher irradiationpower density D_(H). Therefore, the light source drive unit is requiredto switch the two light output levels to drive the laser element withpulse drive or DC drive.

The light source drive unit can employ the switching method. Similar tothe above described example embodiments, in this switching method, thecurrent I_(LD) flowing in the laser element such as LD is monitored by acurrent sensor, and a current detector detects the current monitored bythe current sensor, and transmits the detected current information to acurrent controller. The current controller compares the currentinformation and the reference voltage. If the detected currentinformation is greater than the desired current I_(LD) ⁽⁰⁾, one switchis set ON, and other switch is set OFF to adjust current I_(LD.) If thedetected current information is smaller than the desired current I_(LD)⁽⁰⁾, one switch is set OFF, and other switch is set ON to adjust thedesired current I_(LD.) In this configuration, the current I_(LD) mayfollow a pattern illustrated in FIG. 5. To suppress the ripple amplitudeAR smaller, it is required (1) to reduce the ripple cycle TR and (2) toreduce the ripple gradient LR. As to the reducing the ripple gradient LRt, the inductance of the inductive element L set as the output filter isrequired to be set greater, with which the light source drive unitbecomes greater in size and becomes higher cost.

In view of this issue, a combination of the inductive element L and thecapacitive element C is proposed as the output filter, and applied tothe lighting-use LED. In this configuration, even if the inductance ofthe inductive element L is set smaller, the ripple gradient LR can bereduced in relation with the capacitive element. Therefore, the lightsource drive unit becomes smaller in size, and becomes lower cost.

However, since the LC filter is used as the output filter, the settlingtime such as several milliseconds (ms) to several tens milliseconds (ms)is required to charge the capacitive element, for example, whencontrolling the level of current I_(LD) C.

As to the image writing and erasing application applied to thereversible thermal recording medium, the settling time may causes “imageforming failure” when the recording is started and “image erasingfailure” when the erasing is started. Therefore, the light energy levelduring the settling time is required to be smaller than the desiredlight energy level, or if the light energy level during the settlingtime is greater than the desired light energy level, the light isrequired to be controlled so that the light energy level during thesettling time does not affect the reversible thermal recording medium.

When the output filter is configured as the combination of the inductiveelement L and the capacitive element C, the ripple gradient LR can beset smaller while several milliseconds (ms) is required to stabilize thelight output level from “P_(L)” to “P_(H)” or from “P_(H)” to “P_(L)”when the light output level of semiconductor laser is changed between“P_(L)L” and “P_(H),” and further, the light output level ofsemiconductor laser is required to be monitored whether the light outputlevel of semiconductor laser is stabilized. Therefore, “image formingfailure” may occur on the reversible thermal recording medium when theimage recording is started and “image erasing failure” may occur on thereversible thermal recording medium when the image erasing is started.

The inventors have devised the above described example embodiments inview of these issues.

As to the above described example embodiments, the occurrence ofunintended structural transformation on a process-target object can besuppressed.

Numerous additional modifications and variations for the communicationterminal, information processing system, and information processingmethod, a program to execute the information processing method by acomputer, and a storage or carrier medium of the program are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the disclosure of the presentinvention may be practiced otherwise than as specifically describedherein. For example, elements and/or features of different examples andillustrative embodiments may be combined each other and/or substitutedfor each other within the scope of this disclosure and appended claims.

What is claimed is:
 1. A light irradiation apparatus comprising: anirradiation circuit including a light source to irradiate laser light toa process-target object; a light source driving circuit to drive thelight source; a light source controller to control the light sourcedriving circuit to change a light output level of the light source; anda travelling direction controller to control a travelling direction ofthe light emitted from the light source depending on an operation mode,and a transition mode that one operation mode is being changed toanother mode, wherein the travelling direction controller controls thetravelling direction of the light during the transition mode to adirection that the light does not irradiate the process-target object.2. The light irradiation apparatus of claim 1, wherein the travellingdirection controller includes a deflector to deflect the light emittedfrom the light source.
 3. The light irradiation apparatus of claim 1,wherein the irradiation circuit further includes a scanner to scan theprocess-target object by using the light emitted from the light source,and the travelling direction controller controls the travellingdirection by using the scanner.
 4. The light irradiation apparatus ofclaim 1, further comprising: a light shield disposed at a positiondeviated from a light path of the light extending from the light sourceto the process-target object, and the travelling direction controllerdirects the travelling direction to the light shield during thetransition mode.
 5. The light irradiation apparatus of claim 1, whereinthe travelling direction controller directs the travelling direction ofthe light to a non-effective area where structural transformation theprocess-target object does not occur during the transition mode.
 6. Thelight irradiation apparatus of claim 4, wherein the light shieldperforms heat conversion or light dispersion for at least a part ofincident light that enters the light shield.
 7. The light irradiationapparatus of claim 1, wherein the light source driving circuit includes:an output filter having an inductive element and a capacitive element; apower source electrically connectable with the output filter; a switchto switch electrical conduction and non-conduction between the lightsource and the output filter; a light emission controller to control theswitch based on the light output level; and a current control system tocontrol a current supplied from the power source to the light source viathe output filter based on a set current value of the light outputlevel.
 8. The light irradiation apparatus of claim 7, wherein theprocess-target object is a reversible thermal recording medium, whereinthe light source controller changes the light output level between afirst light output level and a second light output level, the firstlight output level is used for the image recording on the reversiblethermal recording medium, and the second light output level is used forthe image erasing on the reversible thermal recording medium.
 9. Aninformation rewritable system comprising: the light irradiationapparatus claim 8, and a transport circuit to transport one or moreobjects attached with the reversible thermal recording medium on aconveying path while the one or more objects attached with thereversible thermal recording medium faces the light irradiationapparatus at one position the conveying path.
 10. A light irradiationapparatus comprising: an irradiation circuit including a light source toirradiate light to a process-target object; a light source drivingcircuit to drive the light source; a light source controller to controlthe light source driving circuit to change a light output level of thelight source; a light shield moveable between a light block position toblock the light emitted from the light source at least partially, and aretraction position retracted from the light block position; and aposition controller to control a position of the light shield at thelight block position during a transition mode.
 11. The light irradiationapparatus of claim 10, wherein the light shield is an aperture stop. 12.The light irradiation apparatus of claim 10, wherein the light shieldperforms heat conversion or light dispersion for at least a part ofincident light that enters the light shield.
 13. The light irradiationapparatus of claim 10, wherein the light source driving circuitincludes: an output filter having an inductive element and a capacitiveelement; a power source electrically connectable with the output filter;a switch to switch electrical conduction and non-conduction between thelight source and the output filter; a light emission controller tocontrol the switch based on the light output level; and a currentcontrol system to control a current supplied from the power source tothe light source via the output filter based on a set current value ofthe light output level.
 14. The light irradiation apparatus of claim 13,wherein the process-target object is a reversible thermal recordingmedium, wherein the light source controller changes the light outputlevel between a first light output level and a second light outputlevel, the first light output level is used for an image recording onthe reversible thermal recording medium, and the second light outputlevel is used for an image erasing on the reversible thermal recordingmedium.
 15. An information rewritable system comprising: the lightirradiation apparatus of claim 14, and a transport circuit to transportone or more objects attached with the reversible thermal recordingmedium on a conveying path while the one or more objects attached withthe reversible thermal recording medium faces the light irradiationapparatus at one position the conveying path.